Harman/Kardon HK6500. Loudness not working when button is pressed

[Rickedafied]

The two large Capacitors seem to have 3 pins each, I circled them on the photo. I can't tell what pins are negative and positive.

 

[Rickedafied]

I checked the solder on all dark spots, the darkest ones are the components that I had told you that were getting really hot.

 

[KrisBlueNZ]

The two large Capacitors seem to have 3 pins each, I circled them on the photo. I can't tell what pins are negative and positive.

Just measure the voltages on all of the pins. One pin on each capacitor is 0V and you should measure less than 0.01V. One pin on each capacitor is the supply rail and you should measure +40~50V on one of them and -40~50V on the other.

I checked the solder on all dark spots, the darkest ones are the components that I had told you that were getting really hot.

Have you resoldered those connections? They look fine.

 

[Rickedafied]

Ok. C4 and C5 actually have 4 pins each. The forth pin on both capacitors aren't soldered on the board, but I read the voltage of them anyway.

I don't see any writing on the board that tells me what capacitor is C4 or C5, but one capacitors pins read -0.00v, 0.01v, 1 .v and the forth unsoldered pin 0.02v
The other capacitor pins read -0.00v, -0.20v, -1 .v and the forth unsoldered pin -0.72v

From left to right, D1 pins read

1 .v, -0.01v, -0.01v, and -1 .v

Is D1bad? and is it called an Inline Bridge Rectifier ?

How is D1 causing the loudness not to work?

 

[KrisBlueNZ]

I think you must be measuring those voltages wrong. If there was no voltage (or almost no voltage) on any of D1's pins, the whole amplifier would be dead. Try to find a good connection point for the 0V. If you have an RCA phono plug, unscrew the backshell and plug it into a socket on the back panel, and clip your multimeter negative lead onto the ground connection on the plug. This will be the long metal piece with the strain relief clamp at the end, that goes around the cable to support it.

 

[Rickedafied]

Ok. Im getting the same readings on D1 with the phono ground.

 

[Rickedafied]

I tried the amps speaker connections again to make sure the amp is still working and it is, but the loudness button is still not working. Should I replace D1? What is that component and does it show on the schematics the part number?

 

[KrisBlueNZ]

I think there's something wrong with your measurements. The amplifier won't work at all if there's no voltage on the outputs of D1. Here is the relevant part of the schematic.



Near the right I have labelled the +V ("A" marking) and -V ("B" marking) supply rails that supply the power amplifier. The power amplifier will not work at all if these voltages aren't present. They come directly from D1, to the right of the "A" and "B" markings. You can also see C4 and C5. These capacitors smooth those two power supply rails.

So if the amplifier is working at all, at least one, and probably both, of those rails must be present. If your multimeter doesn't measure them, maybe there's something wrong with the multimeter, or the probes, or maybe the circuit board that connects to the RCA phono socket you're using is not connected to the main board, or something like that.

 

[Rickedafied]

My meter is set right?

 

[KrisBlueNZ]

Yes it looks OK. Try measuring the voltage of a battery.

 

[Rickedafied]

Its reading here

 

[Rickedafied]

I used that post with the black wires soldered on it for ground

 

[Rickedafied]

Phono

 

[KrisBlueNZ]

See if you can find where the wires from the mains transformer come onto the board. It will be near to the bridge rectifier. According to the schematic, there's a 2-pin connector called TM403 and another called TM401. Both pins of TM401 are the 0V rail. Connect your meter negative probe to that and try to find some voltages around 40~60V positive and negative on C4 and C5.

 

[Rickedafied]

0.41v on one and the other -0.33v and the rest of the pins are reading zeros still

 

[Rickedafied]

Oops I forgot to turn the amp on but yeah the capacitors are still the same readings as I first told you. No change in voltage

 

[KrisBlueNZ]

That makes no sense. The amplifier would not work at all if there is no voltage across C4 and C5.

How about the AC voltage between the two pins of TM403?

 

[Rickedafied]

AC?

 

[KrisBlueNZ]

AC?

Yes, AC. The voltage across the pins of TM403 comes from the secondary of the mains transformer so it will be AC. The other voltages will be DC though.

 

[Rickedafied]

Oh Ok. Where do place the probes of the meter? Black One on the 0V and the red on each of the TM403 pins?